1. Field of the Invention
The invention concerns a transport device for work-pieces or the like.
2. Description of the Related Art
This type of device is generally well known and is employed in industries with substantially automated processes.
These known transport devices include plate or pallet-shaped work-piece carriers, upon which the material to be transported is deposited. The work-piece carriers are seated upon two drive belts running parallel to each other in the form of belt bands, which for their part are supported upon slide rails. The two belt bands are driven to rotate by a drive motor and thereby take along the work-piece carrier seated thereupon. It is thus necessary that the work-piece carrier frictionally engage the belt bands.
The problem in this regard is the contact occurring between the belt bands and the slide rails, since as a consequence of the high weight of the work-pieces inclusive of the work-pieces carried thereon, a high friction force occurs. This problem is enhanced in the case of a traffic jam of work-piece carriers, which occurs regularly, for example when work-pieces arrive at specific work stations for processing and thus the associated work-piece carriers are stopped. Thereby supplemental frictional forces occur between the belt and the stopped work-piece carrier.
As a consequence of this effect, high drive forces are required in order to ensure operation of the device. Nevertheless, there is a great danger, that in the case of an overload of the conveyor belts the drive motor becomes damaged. There is a further problem in that in the case of continued driving under a high loading a strong fouling occurs. Even if the glide rails are made of stainless steel with a stamped or indented upper surface, this cannot satisfactorily solve the above-mentioned problem. Finally, it can occur in the case of large volume work-pieces, that on the basis of the their larger area, the surface of the work-piece carrier does not have sufficient friction engaging contact and thus can slide on the conveyor belt.
The present invention is thus concerned with the task, of improving a transport device of the above-mentioned type in such a manner, that the above-mentioned disadvantages no longer occur. In particular, a reliable transport of work-piece carriers should be achieved under all operating conditions, without causing an overload of the drive motor.
The invention is based upon the idea, of providing the work-piece carrier upon support rollers, and in this manner to replace the conventional sliding friction, which occurs during transport of the work-piece carrier, with roller friction. Thereby the capacity of the drive means needed to operate the device is substantially reduced. In the case of a continuous operation, this results in a substantial savings and energy costs. Practical tests have found that a savings potential of up to 90% can be achieved.
Preferably two rows of support rollers are provided parallel to each other, wherein the spacing of the two rows is set to correspond to the (standardized) breadth of the workpiece carrier.
Preferably side guides are provided, between which the work-piece carrier is guided with close sideways tolerance. The close tolerance prevents a tipping of the work-piece carrier during the transport movement.
Further variants are concerned with optimizing the design of the drive device.
A first variant envisions the use of a conventional drive belt. As a result of the substantially reduced drive requirement, it is in most cases sufficient to employ a single drive belt, which frictionally engages with the work-piece carriers in the translation direction in a conventional manner.
It has been found to be particularly advantageous when, for the production of the press force necessary for frictional engagement, a multiplicity of sequential, individual slide bars are provided which act upon the drive belt via a spring or biasing device. As a consequence of the spring device, the drive belt is raised slightly, for example 1 to 5 mm. When a work-piece carrier passes over, the respective glide bar is pressed downwards by the weight of the work-piece carrier inclusive of the thereupon situated work-piece, producing a press force which ensures the frictional engagement between the drive belt and the work-piece carrier necessary for the transport. In this manner, the glide bar bars are loaded sequentially one after the other or, as the case may be, in groups, by the work-piece carrier being guided over them. In the case of a traffic jam, the drive belt continues to move below the stopped work-piece carriers. On the basis of the substantially reduced press force, there is, however, no danger of overheating of the drive motor. Also, overall the wear due to friction of the drive is substantially reduced. As a supplemental side effect, it has been determined that the noise level of the overall installation is very much reduced in comparison to the state of the art transport devices.
Preferably, each glide bar is individually spring biased. This makes possible an optimal loading of the drive belt, since the glide pieces are deflected by the work-piece carrier passing over without any reciprocal change-out action.
In a sense of a kinematic reverse, it is likewise possible to run the drive belt over a fixedxe2x80x94that isxe2x80x94not spring biased glide rail and in its place to provide on the work-piece carrier a spring-biased take-along rail, which ensures a defined pressure force for production of the frictional engagement with the drive belt. In this variant also, each work-piece carrier is supported via support rolls.
In a further variant the support rollers are spring-biased. Herein the spring characteristics are so determined, that the main load of the respective impacted support rollers is taken over and a pre-determined residual loading remains for production of the friction-locking contact to the non-yielding or unbiased drive belt.
It is understood that, on the basis of the above-described concept, transport devices can be run in any of various lengths. It can, however, be of advantage, to divide the drive unit into multiple, sequentially arranged, sectional drives, since if the drive belt is too long it must be tensioned too tightly.
A last variant is concerned therewith, to completely dispense with a drive belt in the design of the drive device and instead of this to employ a friction roller drive. Herein at certain separations or distances friction rollers are provided, this being between the support rollers. In this case it must also be ensured, using a spring device, that the friction rollers are pressed against the respective work-piece carriers, in order to produce a friction-locking contact.
According to an inventive concept, so-called xe2x80x9ctranslatorsxe2x80x9d can be constructed, with the help of which, using conventional means and manner, work-piece carriers can be removed perpendicularly to the transport direction.